Table of contents

Preface

The 42nd National Conference on Theoretical Physics (NCTP-42) was held during 31 July - 3 August 2017 in Can Tho, Vietnam.

The NCTP-42 was co-organized by the Institute of Physics, Vietnam Academy of Science and Technology (IOP-VAST) and Can Tho University (CTU) under the support of the Vietnamese Theoretical Physics Society (VTPS).

This meeting belongs to a series of annual theoretical physics conferences that started in 1976.

List of Organizers, Sponsors, Honorary Chair, Chair, Organizing Committee, Local Organizing Committee, Program Committee, Proceedings, Secretariat, List of Participants are available in this pdf.

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

We will present main results of our recent investigations on the validity of cosmic no-hair conjecture proposed by Hawking and his colleagues long time ago in the framework of an anisotropic inflationary model proposed by Kanno, Soda, and Watanabe. As a result, we will show that the cosmic no-hair conjecture seems to be generally violated in the Kanno-Soda- Watanabe model for both canonical and non-canonical scalar fields due to the existence of a non-trivial coupling term between scalar and electromagnetic fields. However, we will also show that the validity of the cosmic no-hair conjecture will be ensured once a unusual scalar field called the phantom field, whose kinetic energy term is negative definite, is introduced into the Kanno-Soda-Watanabe model.

In this paper, we first present briefly to Chameleon mechanism in modified gravity of f(R), then we apply it to modified gravity of polynomial exponential form to find constraints from solar system experiments to parameters of α and β of the model. Results show that the Chameleon mechanism sets strict constraints on α and β parameters as follows: 0 < β < 7.67 × 10⁻¹⁵ and 0 < α < 9 × 10⁻⁷⁵.

Scaling down the bandgap is considered as an essential approach to enhance the performance of tunnel field-effect transistors (TFETs). Using two-dimensional simulations, this study examines the dependence of short-channel effects on the semiconductor bandgap in TFETs. It is shown that the short-channel effect is more severe with using lower bandgap materials although the supply voltage is scaled in parallel with the bandgap. For a given bandgap material, the short-channel effect can be well evaluated by the increase of drain-induced barrier thinning (DIBT) with decreasing the channel length. For different bandgap TFETs, however, their short-channel effects cannot be compared properly by comparing the DIBTs. Adequately considering the effect of bandgap on the TFET scalability is necessary in designing scaled integrated circuits.

In this paper, we present two methods to improve the average fidelity in the quantum teleportation processes to teleport a coherent state via the pair coherent states. We use the measuring of the orthogonal quadrature components in the first protocol and the photon number sum and phase difference in the second. The results show that the average fidelity in the first protocol is enhanced by performing a photon number shifting at a receiver, and F_av can approach to the unit if q becomes very big. In the second protocol, the average fidelity increases with increasing the amplitude of the pair coherent states. It approaches to the unit in the limit of the big amplitude values of the pair coherent states and small of the input state. The average fidelity of both methods is greatly improved comparing with the Gabris-Agarwal protocol and it approaches to unit depending on the parameters involved.

The analytic expressions of the free energy, the mean nearest neighbor distance between two atoms, the elastic moduli such as the Young modulus E, the bulk modulus K, the rigidity modulus G and the elastic constants C₁₁, C₁₂, C₄₄ for substitution alloy AB with interstitial atom C and BCC structure under pressure are derived from the statistical moment method. The elastic deformations of main metal A, substitution alloy AB and interstitial alloy AC are special cases of elastic deformation for alloy ABC. The theoretical results are applied to alloy FeCrSi. The numerical results for alloy FeCrSi are compared with the numerical results for main metal Fe, substitution alloy FeCr, interstitial alloy FeSi and experiments.

The microwave conductivity characteristics of electrolyte solutions have attracted much interest of researchers because a good understanding of their properties plays a key role to study fundamental processes in biology and chemistry. In this work, we consider the solution of sodium chloride as a plasma consisting of ions with water background. Its plasmon frequency is calculated by the jellium theory. The linear dependence of the microwave conductivity on the ion concentration of the electrolyte solutions is explained by a microscopic approach and described by a combination of this plasmon relationship and the simplified Drude formula for dielectric constant. Furthermore, the dependence of the microwave conductivity on the frequency of the salt solution is also examined. We suggest that it obeys the logistic distribution. We found a good agreement between theoretical calculations and experimental data. The values of the damping coefficient γ for the conductive solutions at low frequencies and the cutting frequency are estimated. The linear dependence of the diffusion coefficient on the temperature of the salt solution is also shown, in similarity with the result in the other model. The application of the Drude-jellium model could be done for the other electrolyte solutions in order to study theirs electro-dynamic properties.

This work presents multisubband electron mobility in the polarization semi-parabolic quantum wells (SPQWs) AlN/Al_xGa_1−xN/AlN. First, a theory of multisubband mobility between the lowest two subbands under a uniform external electric field is studied. By using the variation method, the one-dimensional Poisson and Schrödinger equations have been solved within a finite potential barrier model and a bent band figured by all confinement sources (realistic model). Then, we computed and discussed about the effective confining potential profile, the wave function and multisubband mobility. Our result shows that the positive interface polarization charges effect on the distribution of the two-dimensional electron gas (2DEG) in SPQWs so it has great influences on multisubband mobility.

Nuclear level density is studied within a microscopic approach, which is derived based on the exact thermal pairing of the pairing Hamiltonian for the truncated single-particle levels around the Fermi surface in combination with the finite-temperature independent-particle model for the single-particle levels outside the truncated space. The numerical calculations are carried out for ^170,171,172Yb isotopes, whose experimental data are available. The results obtained show that the exact thermal pairing is indeed very important for the valid description of nuclear level density in the low and intermediate regions of excitation energy.

Nanoporous structural prediction is emerging area of research because of their advantages for a wide range of materials science and technology applications in opto-electronics, environment, sensors, shape-selective and bio-catalysis, to name just a few. We propose a computationally and technically feasible approach for predicting Gallium nitride nanoporous structures with hollows at the nano scale. The designed porous structures are studied with computations using the density functional tight binding (DFTB) and conventional density functional theory methods, revealing a variety of promising mechanical and electronic properties, which can potentially find future realistic applications. Their stability is discussed by means of the free energy computed within the lattice-dynamics approach. Our calculations also indicate that all the reported hollow structures are wide band gap semiconductors in the same fashion with their parent's bulk stable phase. The electronic band structures of these nanoporous structures are finally examined in detail.